var x = y = 100

console.log(x);
console.log(y);

let x = 1
const x = 1
var x = 1
function x() {}
class x{}


// 变量名 = 值
lRef = rValue

// 向一个不存在的变量赋值，到底会发生什么？
a = 1

var a = 100
delete a // false
x = 200 
delete x // true
console.log();

eval('var b = 200') // 动态添加，可以删除


